What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world.
That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and
voted up or down.

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted
to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning,
there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

As of this writing, this requires a fairly recent version of util-linux, but is much simpler than the previous alternatives. Basically, lsblk gives a nice, human readable interface to all the blkid stuff. (Of course, I wouldn't recommend this if you're going to be parsing the output.) This command takes all the fun out of the previous nifty pipelines, but I felt I ought to at least mention it as an alternative since it is the most practical.

Don't want to open up an editor just to view a bunch of XML files in an easy to read format? Now you can do it from the comfort of your own command line! :-) This creates a new function, xmlpager, which shows an XML file in its entirety, but with the actual content (non-tag text) highlighted. It does this by setting the foreground to color #4 (red) after every tag and resets it before the next tag. (Hint: try `tput bold` as an alternative). I use 'xmlindent' to neatly reflow and indent the text, but, of course, that's optional. If you don't have xmlindent, just replace it with 'cat'. Additionally, this example shows piping into the optional 'less' pager; note the -r option which allows raw escape codes to be passed to the terminal.

This modifies the output of ls so that the file size has commas every three digits. It makes room for the commas by destructively eating any characters to the left of the size, which is probably okay since that's just the "group".

Note that I did not write this, I merely cleaned it up and shortened it with extended regular expressions. The original shell script, entitled "sl", came with this description:

: '

: For tired eyes (sigh), do an ls -lF plus whatever other flags you give

Of course, some may suggest that fancy new "human friendly" options, like "ls -Shrl", have made Corey's script obsolete. They are probably right. Yet, at times, still I find it handy. The new-fangled "human-readable" numbers can be annoying when I have to glance at the letter at the end to figure out what order of magnitude is even being talked about. (There's a big difference between 386M and 386P!). But with this nifty script, the number itself acts like a histogram, a quick visual indicator of "bigness" for tired eyes. :-)

This is the most straightforward approach: first regexp limits dictionary file to words with thirteen or more characters, second regexp discards any words that have a letter repeated. (Bonus challenge: Try doing it in a single regexp!)

Bash's history expansion character, "!", has many features, including "!:" for choosing a specific argument (or range of arguments) from the history. The gist is any number after !: is the number of the argument you want, with !:1 being the first argument and !:0 being the command. See the sample output for a few examples. For full details search for "^HISTORY EXPANSION" in the bash(1) man page.

Note that this version improves on the previous function in that it handles arguments that include whitespace correctly.

### Start typing a command, say "nm",
$ nm # Realize you've done this before, so press M-p (hold ALT and hit P)
$ nm /usr/bin/wine # Bash completes the line from history! Yay!
### Not the one you wanted? Just keep hitting M-p until you find the one you want.
$ nm /usr/bin/wineserver
### Need to be more specific? Note that the cursor is still after the "nm" that we typed at first, so if we hit "a" it shows this:
$ nma /usr/bin/wineserver
### ...but then, another press of M-p and, voila, we get:
$ nmap -sUT -p- localhost
### Just go ahead and hit enter (you don't need to be at the end of the line) and it runs:
Starting Nmap 7.21 ( http://nmap.org ) at 2018-02-29 09:20 XGT
Interesting ports on localhost (127.0.0.1):
Not shown: 131045 closed ports
PORT STATE SERVICE
22/tcp open ssh
25/tcp open smtp
80/tcp open http
[...]

[Click the "show sample output" link to see how to use this keystroke.]

Meta-p is one of my all time most used and most loved features of working at the command line. It's also one that surprisingly few people know about. To use it with bash (actually in any readline application), you'll need to add a couple lines to your .inputrc then have bash reread the .inputrc using the bind command:

echo '"\en": history-search-forward' >> ~/.inputrc

echo '"\ep": history-search-backward' >> ~/.inputrc

bind -f ~/.inputrc

I first learned about this feature in tcsh. When I switched over to bash about fifteen years ago, I had assumed I'd prefer ^R to search in reverse. Intuitively ^R seemed better since you could search for an argument instead of a command. I think that, like using a microkernel for the Hurd, it sounded so obviously right fifteen years ago, but that was only because the older way had benefits we hadn't known about.

I think many of you who use the command line as much as I do know that we can just be thinking about what results we want and our fingers will start typing the commands needed. I assume it's some sort of parallel processing going on with the linguistic part of the brain. Unfortunately, that parallelism doesn't seem to work (at least for me) with searching the history. I realize I can save myself typing using the history shortly after my fingers have already started "speaking". But, when I hit ^R in Bash, everything I've already typed gets ignored and I have to stop and think again about what I was doing. It's a small bump in the road but it can be annoying, especially for long-time command line users. Usually M-p is exactly what I need to save myself time and trouble.

If you use the command line a lot, please give Meta-p a try. You may be surprised how it frees your brain to process more smoothly in parallel. (Or maybe it won't. Post here and let me know either way. ☺)

Commandlinefu.com is great but has a few bugs when people are submitting new commands:

.

1. There is no preview button. This was a minor inconvenience before, but now is a major problem since new commands won't show up to be edited until they have been moderated.

.

2. White space in the description field and in the comments is almost completely lost. People resort to using periods in between paragraphs to force a line break. Indentation of code is ridiculous.

.

3. Many characters get munged.

.

3a. For example, a less than character in the description gets read as an HTML tag and discarded. In order to type a less than, I've had to type "&lt;" (I hope that comes out right). Unfortunately, when re-editing a command, the HTML entity is turned into a literal less than character, which I have to change back by hand before saving.

3b. Some unicode characters work in the description field, but turn into ugly literal HTML strings when put in the sample output or in an additional command using the $ prefix.

.

For example, here is a unicode character: ❥

Here is the same character after a dollar sign: &#10085;

.

3c. Some unicode characters don't work anywhere. Bizarrely, it appears to be the most commonly needed ones, such as Latin-1 accented characters. Here are some examples,

.

Bullet: ?, Center dot: ?, Umlaut u: ?.

.

4. Here is an example of the greater than, >, and less than,

.

5. Commandlinefu used to abbreviate long descriptions on the front page and had a "more..." button so that people could read the rest if they wanted. That's a good feature as it encourages people to explain their commands more fully. Either, the feature has gone missing, or, perhaps, I was just hallucinating it existed in the first place. If the former, please bring it back, If the latter, please implement this great new feature I just thought up.

.

6. Tags cannot include Unicode characters. If you try to type one in, the cursor will just spin and spin as it attempt to look up if that tag exists already. For example, try typing Ctrl+Shift+u 2 7 6 5 SPC as a tag name.

[Update! Thanks to a tip from ioggstream, I've fixed both of the bugs mentioned below.]

You, yes, 𝙔𝙊𝙐, can be the terror of the Internet! Why use normal, boring bullet points in your text, when you could use a ROTATED HEAVY BLACK HEART BULLET (❥)!? (Which would also be an awesome band name, by the way).

﻿

This script makes it easy to find unusual characters from the command line. You can then cut and paste them or, if you're using a GTK application, type Control+Shift+U followed by the code point number (e.g., 2765) and then a SPACE.

﻿

USAGE: Put this script in a file (I called mine "ugrep") and make it executable. Run it from the command line like so,

﻿

ugrep heart

﻿﻿

The output will look like this,

﻿

☙ U+2619 REVERSED ROTATED FLORAL HEART BULLET

♡ U+2661 WHITE HEART SUIT

♥ U+2665 BLACK HEART SUIT

❣ U+2763 HEAVY HEART EXCLAMATION MARK ORNAMENT

❤ U+2764 HEAVY BLACK HEART

❥ U+2765 ROTATED HEAVY BLACK HEART BULLET

❦ U+2766 FLORAL HEART

❧ U+2767 ROTATED FLORAL HEART BULLET

⺖ U+2E96 CJK RADICAL HEART ONE

⺗ U+2E97 CJK RADICAL HEART TWO

⼼ U+2F3C KANGXI RADICAL HEART

﻿

You can, of course, use regular expressions. For example, if you are looking for the "pi" symbol, you could do this:

﻿

ugrep '\bpi\b'

﻿

REQUIREMENTS: Although this is written in Bash, it assumes you have Perl installed because it greps through the Perl Unicode character name module (/usr/lib/perl5/Unicode/CharName.pm). Note that it would not have made more sense to write this in Perl, since the CharName.pm module doesn't actually include a subroutine for looking up a character based on the description. (Weird.)

﻿

BUGS: In order to fit this script in the commandlinefu limits, a couple bugs were added. ① Astral characters beyond the BMP (basic multilingual plane) are not displayed correctly, but see below. ② Perl code from the perl module being grepped is sometimes extraneously matched.

﻿

MISFEATURES: Bash's printf cannot, given a Unicode codepoint, print the resulting character to the terminal. GNU's coreutils printf (usually "/usr/bin/printf") can do so, but it is brokenly pedantic about how many hexadecimal digits follow the escape sequence and will actually die with an error if you give the wrong number. This is especially annoying since Unicode code points are usually variable length with implied leading zeros. The CharNames.pm file represents BMP characters as 4 hexits, but astral characters as 5. In the actual version of this script that I use, I've kludged around this misfeature by zero-padding to 8 hexits like so,

﻿

/usr/bin/printf "\U$(printf "%08x" 0x$hex)"

﻿

TIP 1: The author recommends "xsel" for command line cut-and-paste. For example,

﻿

ugrep biohazard | xsel

﻿

TIP 2: In Emacs, instead of running this command in a subshell, you can type Unicode code points directly by pressing Control-Q first, but you'll likely want to change the default input from octal to hexadecimal. (setq read-quoted-char-radix 16).

﻿

TIP 3: Of course, if you're using X, and you want to type one of the more common unusual characters, it's easiest of all to do it with your Compose (aka Multi) key. For example, hitting [Compose] <3 types ♥.

"OneBox" is Google's term for that box that appears before the organic search results that has useful information that Google thinks you might be looking for (mathematical calculations, weather, currency conversions, and such). I'm not actually using OneBox correctly, but that's because I'm not sure that there is a "correctly". I looked for a command line API, but couldn't find one, so I settled on parsing stdout from the fantastic w3m web browser. I use the sed script to show only the first hit by deleting everything from the beginning of the file until it sees " 1." and then deleting everything from " 2." to the end of the file. Ugly and fragile, yes, but it works fine.

.

BUG1: w3m represents the picture of the sun rising, "weather_sunset-40.gif" as "[weat]" which is slightly confusing and probably should be removed.

.

BUG2: The output is more easily readable by a human, which means it's less useful for scripting.

I woke up around midnight with an urge to do some late night hacking, but I didn't want a bright monitor screwing up my body's circadian rhythm. I've heard that at night blue (short wavelength) lights are particularly bad for your diurnal clock. That may be a bunch of hooey, but it is true that redder (longer wavelength) colors are easier on my eyes at night.

This command makes the screen dimmer and adjusts the gamma curves to improve contrast, particularly darkening blues and greens (Rɣ=2, Gɣ=3, Bɣ=4). To reset your screen to normal, you can run this command:

Note: The sed part is fragile and wrong. I'm doing it this way because of a misfeature in xrandr(1), which requires an output be specified but has no programmatic way of querying available outputs. Someone needs to patch up xrandr to be shell script friendly or at least add virtual outputs named "PRIMARY" and "ALL".

.

Todo: Screen should dim (gradually) at sunset and brighten at sunrise. I think this could be done with a self-resubmitting at job, but I'm running into the commandlinefu 127 character limit just getting the sunrise time:

I hope some clever hacker comes up with a command line interface to Google's "OneBox", since the correct time shows up as the first hit when googling for "sunrise:cityname".

.

[Thank you to @flatcap for the sed improvement, which is much better than the head|tail|cut silliness I had before. And thank you to @braunmagrin for pointing out that the "connected" output may not be on the second line.]

This is like ping -a, but it does the opposite. It alerts you if the network is down, not up. Note that the beep will be from the speaker on the server, not from your terminal.

Once a second, this script checks if the Internet is accessible and beeps if it is not. I define the Net as being "UP", if I can ping Google's public DNS server (8.8.8.8), but of course you could pick a different static IP address. I redirect the beep to /dev/console so that I can run this in the background from /etc/rc.local. Of course, doing that requires that the script is run by a UID or GID that has write permissions to /dev/console (usually only root).

Question: I am not sure if the -W1 flag works under BSD. I have only tested this under GNU/Linux using ping from iputils. If anybody knows how portable -W is, please post a comment.

In general, this is actually not better than the "scrot -d4" command I'm listing it as an alternative to, so please don't vote it down for that. I'm adding this command because xwd (X window dumper) comes with X11, so it is already installed on your machine, whereas scrot probably is not. I've found xwd handy on boxen that I don't want to (or am not allowed to) install packages on.

NOTE: The dd junk for renaming the file is completely optional. I just did that for fun and because it's interesting that xwd embeds the window title in its metadata. I probably should have just parsed the output from file(1) instead of cutting it out with dd(1), but this was more fun and less error prone.

NOTE2: Many programs don't know what to do with an xwd format image file. You can convert it to something normal using NetPBM's xwdtopnm(1) or ImageMagick's convert(1). For example, this would work: "xwd | convert fd:0 foo.jpg". Of course, if you have ImageMagick already installed, you'd probably use import(1) instead of xwd.

NOTE3: Xwd files can be viewed using the X Window UnDumper: "xwud <foo.xwd". ImageMagick and The GIMP can also read .xwd files. Strangely, eog(1) cannot.

NOTE4: The sleep is not strictly necessary, I put it in there so that one has time to raise the window above any others before clicking on it.

Yes, You could do it in the GIMP or even use Inkscape to auto-align the clones, but the command line is so much easier.

NOTE: The +clone and -clone options are just to shorten the command line instead of typing the same filename eight times. It might also speed up the montage by only processing the image once, but I'm not sure. "+clone" duplicates the previous image, the following two "-clone"s duplicate the first two and then the first four images.

NOTE2: The -frame option is just so that I have some lines to cut along.

BUG: I haven't bothered to calculate the exact geometry (width and height) of each image since that was not critical for the visa photos I need. If it matters for you, it should be easy enough to set using the -geometry flag near the end of the command. For example, if you have your DPI set to 600, you could use "-geometry 800x1200!" to make each subimage 1⅓ x 2 inches. You may want to use ImageMagick's "-density 600" option to put a flag in the JPEG file cuing the printer that it is a 600 DPI image.

BUG2: ImageMagick does not autorotate images based on the EXIF information. Since the portrait photo was taken with the camera sideways, I made the JPEG rotate using jhead like so: jhead -autorot 2007-08-25-3685.jpg

The same as the other two alternatives, but now less forking! Instead of using '\;' to mark the end of an -exec command in GNU find, you can simply use '+' and it'll run the command only once with all the files as arguments.

This has two benefits over the xargs version: it's easier to read and spaces in the filesnames work automatically (no -print0). [Oh, and there's one less fork, if you care about such things. But, then again, one is equal to zero for sufficiently large values of zero.]

I noticed some spammer posted an advertisement here for "not bad" encryption. Unfortunately, their software only runs under Microsoft Windows and fails to work from the commandline. My shell script improves upon those two aspects, with no loss in security, using the exact same "military-grade" encryption technology, which has the ultra-cool codename "ROT-13". For extra security, I recommend running ROT-13 twice.

Just a quick hack to give reasonable filenames to TrueType and OpenType fonts.

I'd accumulated a big bunch of bizarrely and inconsistently named font files in my ~/.fonts directory. I wanted to copy some, but not all, of them over to my new machine, but I had no idea what many of them were. This script renames .ttf files based on the name embedded inside the font. It will also work for .otf files, but make sure you change the mv part so it gives them the proper extension.

BUGS: Well, like I said, this is a quick hack. It grew piece by piece on the command line. I only needed to do this once and spent hardly any time on it, so it's a bit goofy. For example, I find 'rev | cut -f1 | rev' pleasantly amusing --- it seems so clearly wrong, and yet it works to print the last argument. I think flexibility in expressiveness like this is part of the beauty of Unix shell scripting. One-off tasks can be be written quickly, built-up as a person is "thinking aloud" at the command line. That's why Unix is such a huge boost to productivity: it allows each person to think their own way instead of enforcing some "right way".

On a tangent: One of the things I wish commandlinefu would show is the command line HISTORY of the person as they developed the script. I think it's that conversation between programmer and computer, as the pipeline is built piece-by-piece, that is the more valuable lesson than any canned script.

Looks up a word on merriam-webster.com, does a screen scrape for the FIRST audio pronunciation and plays it.

USAGE: Put this one-liner into a shell script (e.g., ~/bin/pronounce) and run it from the command line giving it the word to say:

pronounce lek

If the word isn't found in merriam-webster, no audio is played and the script returns an error value. However, M-W is a fairly complete dictionary (better than howjsay.com which won't let you hear how to pronounce naughty words).

ASSUMPTIONS: GNU's sed (which supports -r for extended regular expressions) and Linux's aplay. Aplay can be replaced by any program that can play .WAV files from stdin.

KNOWN BUGS: only the FIRST pronunciation is played, which is problematic if you wanted a particular form (plural, adjectival, etc) of the word. For example, if you run this:

pronounce onomatopoetic

you'll hear a voice saying "onomatopoeia".

Playing the correct form of the word is possible, but doing so might make the screen scraper even more fragile than it already is. (The slightest change to the format of m-w.com could break it).

This is a minimalistic version of the ubiquitious Google definition screen scraper. This version was designed not only to run fast, but to work using BusyBox. BusyBox is a collection of basic Unix tools that have been compiled into a single binary to save space on tiny installations of Unix. For example, although my phone doesn't have perl or the GNU utilities, it does have BusyBox's stripped down versions of wget, tr, and sed. It turns out that those tools suffice for many tasks.

Known Bugs: This script does not handle HTML entities at all. I don't think there's an easy way to do that within BusyBox, but I'd love to see it if someone could do it. Also, this script can only define a single word, not phrases. (Well, you could if you typed in %20, but that'd be gross.) Lastly, this script does not show the URL where definitions were found. Given the randomness of the Net, that last bit of information is often key.

Comcast is an ISP in the United States that has started hijacking DNS requests as a "service" for its customers. For example, in Firefox, one used to be able to do a quick "I'm Feeling Lucky" Google search by typing a single word into the URL field, assuming the word is not an existing domain when surrounded by www.*.com. Comcast customers never receive the correct NX (non-existent domain) error from DNS. Instead, they are shown a page full of advertising. There is a way to "opt out" from their service, but that requires having the account password and the MAC address of your modem handy. For me, it was easier just to set static DNS servers. But the problem is, which ones to choose? That's what this command answers. It'll show you the three _non-hijacked_ Comcast DNS servers that are the shortest distance away.

Perhaps you don't have Comcast (lucky you!), but hopefully this command can serve as an example of using netselect to find the fastest server from a list. Note that, although this example doesn't show it, netselect will actually perform the uniq and DNS resolution for you.

This command creates and burns a gapless audio CD with 99 tracks. Each track is a 30 second sine wave, the first is 1 Hz, the second 2 Hz, and so on, up to 99 Hz. This is useful for testing audio systems (how low can your bass go?) and for creating the constant vibrations needed to make non-Newtonian fluids (like cornstarch and water) crawl around.

Note, this temporarily creates 500MB of .cdda files in the current directory. If you don't use the "rm" at the end of the command, you can burn more disks using